1. Field of the Invention
The invention relates to an interface circuit which can automatically (or autonomously) adjust a slew rate into a predetermined value established by an external terminal resistance, regardless of conditions including a process condition.
2. Description of the Related Art
Adjusting a slew rate of an output signal of an interface circuit is important to solve a problem of signal reflection which is caused to occur in connection with the interface circuit. A technology related to the problem has been developed.
A slew rate detector which can adjust a slew rate in an interface circuit is proposed in an article (FIG. 7) xe2x80x9cA 2.6 GBYTE/s Multipurpose Chip-to-Chip Interfacexe2x80x9d, SOLID-STATE CIRCUIT, Vol. 33, No. 11, November 1998.
The proposed slew rate detector provides a reference clock to a slew rate control logic and starts to search a process condition and other environmental conditions in response to a trigger signal. Specifically, the slew rate detector detects output signals at two points after a signal is entered to an NMOS Delay Chain, and the detected signals are provided to a flip-flop circuit (FF) at a timing defined by a sample clock. Then, the detector searches a process condition and other environmental conditions by calculating a differential delay between the signals, and generates a slew rate code corresponding to the searched conditions.
As described above, conventional interface circuits generally search a process condition and other environmental conditions, and generate a slew rate code according to the searched conditions. This means that the slew rate code inevitably depends on the searched conditions. Therefore, there is no conventional interface circuit which can determine and generate a slew rate code independent of these conditions. In other words, a positive decision of a slew rate has not been made in any conventional circuit.
It is, therefore, an object of the invention to provide an interface circuit which determines a slew rate according to a current value of a current source established by an external terminal resistance, independently of conditions including a process condition.
It is another object of the invention to provide an interface circuit which automatically adjusts an initial rise time and an initial rise voltage of an output signal, after adjustment of an impedance and a slew rate.
According to a first aspect of the invention, there is provided a slew rate adjusting circuit comprising a pre buffer unit which receives an input signal, a slew rate control unit which determines a current value of a current supplied to the pre buffer unit and automatically controls a slew rate of the input signal, and a main buffer unit which receives the input signal from the pre buffer unit and, in response to receiving of the input signal, outputs an interface output with a slew rate controlled by the slew rate control unit.
According to a second aspect of the invention, there is provided a method of adjusting a slew rate between an input signal and an output signal. The method comprises the steps of variably controlling a value of a drive current by using a relationship between the value of the drive current and the slew rate, and adjusting the slew rate based on the value of the drive current.
According to a third aspect of the invention, there is provided a method of adjusting a slew rate comprising the steps of receiving, at a pre buffer unit, an input signal, determining a current value of a current provided to the pre buffer unit and automatically controlling a slew rate of the input signal, and receiving the input signal from the pre buffer unit, and outputting an interface output at the controlled slew rate in response to inputting of the input signal.
According to a fourth aspect of the invention, there is provided a recording medium readable by a computer, tangibly embodying a program of instructions executable by the computer to perform a method of adjusting a slew rate comprising the steps of receiving, at a pre buffer unit, an input signal, determining a current value of a current provided to the pre buffer unit and automatically controlling a slew rate of the input signal, and receiving the input signal from the pre buffer unit, and outputting an interface output at the controlled slew rate in response to inputting of the input signal.
According to a fifth aspect of the invention, there is provided a computer data signal embodied in a carrier wave and representing a sequence of instructions which, when executed by a processor, cause the processor to perform a method of adjusting a slew rate comprising the steps of receiving, at a pre buffer unit, an input signal, determining a current value of a current provided to the pre buffer unit and automatically controlling a slew rate of the input signal, and receiving the input signal from the pre buffer unit, and outputting an interface output at the controlled slew rate in response to inputting of the input signal.